Neuro - MS Tutorial Flashcards
What is multiple sclerosis?
Autoimmune disorder
Results in loss of myelin from neurons of central nervous system i.e. brain + spinal chord
What are the main symptoms of MS?
Blurred vision Fatigue Difficulty walking Numbness or tingling (paraesthesia) in different parts of the body Muscle stiffness and spasms
What is an M-wave?
Electrical stimulus of an appropriate intensity to a peripheral nerve can activate sensory + motor axons.
Activation of motor axons cause action potentials to travel along the nerve to cause muscle contraction, a twitch.
This fast response is the M-wave.
What is a H-reflex (wave)?
Same stimulus can cause activation of sensory axons (subject feels stimulus)
Action potentials can travel along the nerve to the spinal cord and can activate lower motor neurons.
Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch.
This is a reflex activation of the muscle.
This response is called the H-reflex.
What is the F-wave?
A large electrical stimulus that causes activation of motor axons to conduct antidromically.
First, the action potentials travel along the motor nerve to the spinal cord (i.e. in the opposite way to normal). These cause the lower motor neurons in the spinal cord to become activated. Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch.
What is orthodromic activation?
Activation travelling in the normal direction in a nerve fibre
What is antidromic activation?
Travelling in the opposite direction to that normal in the nerve fibre
How are all the waves recorded?
Using EMG (electromyography)
How can you illicit cortical motor stimulation?
Using TMS (transcranial magnetic stimulation)
How does TMS cause brain stimulation? What is the name of the exact response it produces?
Activation of the upper motor neurons causes action potentials to travel along the entire motor pathway (upper and lower motor neurons) to cause muscle contraction.
This EMG response is called an MEP (motor evoked potential)
What is an MEP?
Motor evoked potential
The whole potential from activation of upper motor neuron and lower motor neuron.
What is TMCT?
Total motor conduction time
Time taken from brain to muscle (MEP latency)
What is PMCT?
Peripheral motor conduction time
Time taken from spinal cord to muscle along motor axon
How do you calculate PMCT?
PMCT = (M latency + F latency - 1) / 2
Why do you - 1 in the PMCT calculation?
-1 is the estimated time for the action potentials arriving at the lower motor neuron cell body to turn around
